Subscription count must be public on YouTube
Synced video limits: 80 under 600 subs, 200 under 800 subs, 250 under 1K subs, 400 under 5K subs, 500 under 10K, and 1K videos for all higher sub counts.
Video length limits: 30 minutes under 500 subs, 1hr under 1K subs, and 2hr for all higher sub counts. Longer videos will be skipped.
Videos bigger than 2GB will be synced at lower quality (720p, 480p, ...)
Due to high demand, you will be only be synced if you have at least 300 subscribers.